Combustion air preheater



June 27, 1961 F. w. RIEHL COMBUSTION AIR PREHEATER 4 Sheets-Sheet 1Filed Dec. 23, 1957 F l'g.

INVENTOR. Frederick W. Rieh/ ATTORNEYS June 27, 1961 F. w. RIEHLCOMBUSTION AIR PREHEATER 4 Sheets-Sheet 2 Filed Dec. 23, 1957 1 aIZIIFQHRIHQEE Eli III F iqs INVENTOR. Frederick W. Rieh/ ATTORNEYS June27, 1961 F. w. RIEHL 2,989,952

COMBUSTION AIR PREHEATER Filed Dec. 23, 1957 4 Sheets-Sheet 3 INVENTOR.Frederick W Rieh/ ATTORN EYS F. W. RlEHL COMBUSTION AIR PREHEATER June27, 1961 I 4 Sheets-Sheet 4 Filed Dec. 23, 1957 BY M ATTORNEYS h m R W kw United States Patent" 2,989,952 COMBUSTION AIR PREl-IEATER FrederickW. Riehl, 2347 Albion St., Denver, Colo. Filed Dec. 23, 1957, Ser. No.704,449 9 Claims. (Cl. 1221) This invention relates to air heatingequipment and particularly to an improved air preheater for heating airsupplied to the furnaces for combustion within the boilers of powerplants.

The present application is a continuation-in-part of the presentinventors parent application Serial No. 210,417 filed February 10, 1951which was issued on December 24, 1957 as Patent No. 2,817,321, and of adivisional application thereof, Serial No. 601,670 filed August 2, 1956now abandoned.

Various types of heat exchangers have been employed heretofore forpreheating the air supplied to the combustion apparatus of power plants.While these preheater-s have been satisfactory for specific purposes andwithin predetermined ranges of operation, it is desirable to provideimproved apparatus to secure more effective use of the temperaturegradients available and to provide a greater degree of control of thetemperature of the preheated air together with assuring a minimumpressure drop of air and gas flow. Accordingly it is an object of thisinvention to provide an air preheater of improved and efficient design.

It is another object of this invention to provide an improved airpreheater for boiler furnaces and the like which affords more effectivecontrol of the temperature of the preheated air over wide ranges of heatloads.

It is a further object of this invention to provide an improved airpreheater for boiler furnaces and the like which affords variablecontrol of the heated air temperature.

In carrying out the objects of this invention in one embodiment thereofa preheating unit is provided which comprises a multiplicity of straightgas tubes arranaged vertically in the gas flow passage and sealed inopposite end plates, the space between the plates and around the tubesproviding an air heating passage. The air heating passage is providedwith an inlet and an outlet substantially coextensive with the length ofthe tubes and located in the sides of the preheater together with abaflie arrangement for directing the air to be heated about the tubestransversely of the direction of passage of the combustion gases. Thebaffle arrangement is further constructed to provide :a steadilyincreasing cross sectional area for the air path from the inlet to theoutlet and thus to provide increased volume for the heated and expandedair. In another embodiment the arrangement of air and gas passages. issimilar to that of the first embodiment and includes a division of theair circulating zone into two separate compartments in which thecirculating baffle arrangement is opposite so that in one compartmentthe air to be heated flows around the tubes in an opposite direction tothat of the other compartment. In addition an air damper control isprovided so that the two compartments may be connected for either seriesor parallel flow, the flow paths being selected so that the loadings ofthe two compartments are substantially equal. Further control of thepreheater is effected by a damper arranged to shut off selected ones ofthe gas tubes for securing more effective use of the gas tube surfaceduring light loads.

The features of novelty which. characterize the invention will bepointed out with particularity in the claims annexed to and forming apart of this. specification The invention itself, however, togetherwith. further objects and advantages thereof, will be better understoodupon 2,989,952 Patented June 2'7, 1961 reference to the followingdescription taken in connection with the accompanying drawings in which:

FIG. 1 is an elevational view partly in section of a turbine power plantboiler provided with a preheater em bodying this invention;

FIG. 2 is a sectional view along the line 2-2 of FIG. 1 showing thepreheater construction;

FIG. 3 is an enlarged vertical section view of a preheater similar tothat shown in FIG. 1 including a modificartion of the invention;

FIG. 4 is a sectional view along the line 44 of FIG. 3;.

FIG. 5 is a sectional view along the line 5-5 of FIG. 3;

FIG. 6 is an enlarged perspective view partially broken away showing theair preheater of FIG. 3; and

FIGS. 7 and 8 are perspective views similar to FIG. 6

7 illustrating the two conditions of air flow of the preheater.

Referring now to the drawings the power plant boiler and stack assemblyillustrated in FIGS. 1 and 2 is the same unitary stack and boiler asthat disclosed in the above-identified parent and divisionalapplications. The power plant as illustrated in. FIG. 1 comprises acombined boiler and stack assembly arranged in a vertical cylindricalshell 10 which acts both as a supporting structure for the boiler andauxiliary units and as the stack. Steam generated in the assembly 10 isdischarged through an outlet 11 to a steam turbine 12 through suitablesupply lines which have not been illustrated. The turbine 12 ismountedon a platform 13 supported on columns 14 immediately adjacent theboiler assembly 10. A plurality of burners 15 which may employ eithergaseous or' liquid fuel are arranged in a ring about the lower portionof the boiler which provides a combustion zone 16. The inside of thecylinder 10 is lined with Water tubes 17 which provide the active boilersurface and extend from a lower header or mud drum 18 to an upper steamdrum 19, certain of the tubes 17 being bent out as indicated at 17' toprovide screen tubes which protect banks of superheater tubes 21 fromthe intense heat of the hot combustion gases rising through the centerof the stack. The superheater tubes 21 connect the steam drum 19 and atoroidal superheated steam header 21 arranged about the outside of thestack about midway between the drums 18 and 19, and the dischargeconduit 11 is connected to the superheater header 21' to supplysuperheated steam to the turbine. An air preheater 22 is provided in thestack 10 above the boiler zone, the stack providing the side walls orenclosure of the preheater. Fresh air supplied to the heater through aside inlet 20 is connected through the air heater and thence to apassage 23 and downwardly to a toroidal air supply manifold 24; themanifold ex tends about the stack adjacent the burners 15 and isconnected to supply the preheated combustion air to the burners. Thecombustion gases rising through the stack pass through the air'preheater22- and then are conducted through a dust collector or fly ash removalsection 25' and thence-out the top of the stack. As illustrated thepreheater 22 comprises a multiplicity of vertically ar-' ranged parallelgas tubes 27 which lie in the path of the hot combustion gases risingthrough the stack and are sealed into lower and upper plates 28 and 29so that all the gases rising through the stack must pass through thetubes'27l The great number of small tubes 27 assures a large heattransfer surface While providing ample gas flow capacity withoutrequiring that the tubes have great length. The plates 28' and 29 dividethe space about the tubes into a separate compartment and as shown inFIG- URE 2 this compartment is in open communication with the intakeconnection 20 and with a discharge connection or outlet 31. whichconducts the heated air directly into the conduit 23. The inlet 20 andthe outlet 31 extend for substantially the full length of the tubes 27and are so arranged that the fresh air admitted to the inlet 20 isdirected through a path of expanding cross section around the tubes 27.The path of the air through the preheater is determined by an uprightbaffie 33 which extends between the plates 28 and 29. and is curved asshown to direct the air from the inlet 20 horizontally around the tubesin the center and thence to the outside and around the compartmenttoward the outlet, a shorter section of baffie 34 being provided tocooperate with the bafile 33 to direct the air initially toward thecenter of the preheater. It will thus be apparent that as the air passesthrough the compartment between the plates 28 and 2.9 and is heated itexpands and the passageway from the inlet 20 to the outlet 31 isenlarged to allow for this expansion and provide more uniform airvelocity through the flow path. The fresh air may be supplied to thepreheater through the inlet 20 by a suitable fan or forced draftequipment (not shown). The gradually expanding passage through thepreheater materially reduces the frictional drag therethrough so that alarger quantity of air may be delivered to the burners Without the useof more than a minimum of external power, thus avoiding various velocitypressure drop conditions. The air traveling through the generallyhelical passage around the gas tubes about the baifies33 and 34 willhave considerable turbulence thereby facilitating the rate of heattransfer between the walls of the tubes 27 and the air being heated.

The modification of the invention illustrated in FIGS. 3 to 8,inclusive, employs a preheater using essentially the same arrangement ofcombustion gas tubes and air baffles as that illustrated in FIGS. 1 and2 and also includes additional features whereby the preheating of theair may be accomplished more efliciently and may be controlled inaccordance with changes in the load on the boiler. In view of thesimilarity of construction, corresponding parts of the modification ofFIGS. 3 to 8 have been designated by the same numerals as those employedin FIGS. 1 and 2 with the addition of the sufiix letter a.

Referring now to FIG. 3 it will be noted that the preheater unit 22acomprises a pair of spaced plates 28a and 29a extending across thecasing 10a and connected by a multiplicity of tubes 27a which providethe sole gas passages between the portion of the stack 10a belowv thepreheater to that above the preheater. The preheater is supported at itsupper periphery by securing the plate 29:: to the side wall of the stackso that it is suspended within the stack; additional support for thepreheater is provided by a plurality of rods 36 secured to the plate 29aat their lower ends and at their upper ends to the inner rim of afrusto-conical baffle 37. The baffle defines a central passageway upthrough the stack above the plate 29a and helps to maintain constant gasvelocity. The frustoconical form of the baffle 37 provides a securesupport for the preheater and also acts as the lower wall of the fly ashremover 25a; The fly ash remover or dust collector 25a includes a secondfrusto-conical bafiile 38 inverted with respect to the first baflle andconnected to the first bafile by a cylindrical wall 39 within which isarranged a single plate spiral or helical bafie 41 for imparting atwisting movement of the gases rising through the center of the stack.The dust collector 25a is closed by a plate 42 having a circular opening43 at the center which may be closed by a damper 44 in order to directthe gases rising from the baflle 41 through semi-circular openings intoa plurality of tubes 45 and thence downwardly into the ring-shapedchamber formed between the baffies 37, 38 and 39. The gas from thischamber is discharged through inner tubes 46 which pass upwardly throughthe plate 42 to the top of the stack to atmosphere. Thus the gases whichare directed through the tubes 45 are caused to move downwardly and tobe reversed suddenly which throws out from the gases any solid particlesuch as fly ash or dust contained therein. The space hetween preheateroutlet and stack shell provides a large storage space for fly ash. Whenliquid fuel is being employed or when for other reasons it is notdesired to use the dust collector tthe damper 44 is opened so that itlies in the position shown whereupon the gases move directly upwardly toatmosphere through the center of the stack thus short circuiting thedust collector. Ash or dust collected in the unit 24a and whichaccumulates around the bottom of the baffle 37 may be removed throughoperation of an. automatic ash removal system indicated at 47.

The space about the tubes 27a and the unit 22a is divided into upper andlower compartments by a bafile plate 49 which is similar in form to theplates 28a and 29a and the vertical baffies in the two compartments arearranged to circulate air in a horizontal plane in opposite circulardirections, the air being supplied and removed through a duct and damperassembly designated generally by the numeral 50 at its side. In order toallow for expansion and contraction of the unit 22a due to change oftemperature about the tubes 27a, the lower plate 28a is connected to theside walls of the casing 10a by a flexible joint 51 of pleated metalwhich is sealed between the plate 28a and an annular ring or shoulder 52secured to the walls of the casing 10 below the unit 22a. The shoulder52 also acts as a rest for a rotary soot blower 53 which is rotatablymounted on a bearing 530: at the center of the stack and has its outerend supported on a track or shoulder 52. The soot blower 53 is actuatedby steam supplied through a conduit 54 and is self rotated by a jet ofsteam passing through one or more openings 55 in the side of the arm 53;the high. velocity steam for removing the fly ash from the tubes 27a isdirected upwardly through a plurality of jets 56 on the topside of thearm 53. When the unit 22a is employed in a combined draft stack andboiler assembly located in upper half thereof as illustrated, the flyashes removed during the idle periods of the system fall to the bottomwhere they are collected in an ash hopper 58 shown at the bottom of thecasing 10 in FIG. 1. When the unit 22a is employed in other applicationsa suitable ash hopper may be located conveniently close to the bottom ofthe unit directly below whatever inlet ducts are provided for supplyingthe combustion gases which are to pass through the unit.

The structural arrangement of the bafiles within the upper and lowercompartments of the unit 22a is shown in FIGS. 4 and 5. In the uppercompartment as shown in FIG. 4 a baffle 59 extends from the right handside of an inlet opening 60 and curves around the center ofthecompartment and cooperates with a straight baffle 61 to provide agradually expanding passageway for the air to be heated in the samemanner as the baffles 33 and 34 of FIG. 2. The air is discharged fromthe upper com partment through an outlet 62, both the inlet and theoutlet communicating with ducts within the assembly 50.

The lower section of the compartment shown in FIG. 5 is provided with acurved baffle 63 which cooperates with a straight baflle 64 to provide agradually increasing air path for the air admitted to the compartmentthrough an inlet 65 and passing around the battles to an outlet 66, theinlet and the outlet communicating with passages in the asssembly 50 ina manner similar to that of the upper compartment shown in FIG. 4. Itwill be noted that the direction of passage or rotation of the air goingthrough the upper and lower compartments is opposite, the inlet to theupper compartment being directly above the outlet to the lowercompartment and vice versa.

This opposite air flow arrangement in the two compartments tends toequalize the heat transfer along the combustion gas tubes 270: so that asubstantially uniform heat transfer characteristic is provided for thepreheater. The manner in which this is accomplished will be understoodby considering a single tube 27a which must pass through bothcompartments. If the tube is located so that it passes through the inletzone of the lower compartment it will pass through the outlet zone ofthe upper compartment, thus the tube will lie in the lower airtemperature zone of the lower compartment and in the higher airtemperature zone of the upper compartment. 0n the other hand a tubewhich passes through the outlet or higher air temperature zone of thelower compartment will pass through the inlet or lower air temperaturezone of the upper compartment. This arrangement provides a desirablecounterflow relationship of the air paths. and combustion gas paths andassures greater effectiveness of the heat transfer system.

The upper and lower compartments are connected with control ducts in theassembly 50 in a manner such that they may be connected either in seriesor in parallel relationship with respect to the, flow path of the air tobe preheated. This arrangement facilitates the control of the airtemperature in accordance with the load demand on the system.

The structural arrangement of the damper control and air supply andexhaust assembly 50 is shown in FIGS. 6, 7 and 8. As illustrated inthese figures the assembly 50 includes a generally rectangular box-likestructure, the rear edge portions of the walls of which are shaped toconform to the curved wall of the cylindrical casing 10a so that thecasing constitutes the back wall of the assembly. The structure isprovided with an air intake duct 67 and a discharge duct 68 which isarranged to be connected to a conduit for conveying the preheated air tothe burners of a furnace in the same manner as the duct 23 illustratedin FIG. 1, The inlet duct 67 communicates directly with an inletpassageway extending vertically from the duct to a horizontal cross wallor partition 70 spaced from the closed top wall, 69 of the unit 50, theinlet passageway being designated generally at 71 on the drawing. Theduct 71 communicates directly with an inlet chamber 72. in front of theinlet 60 to the upper air compartment, these passages being open at alltimes. The lower end of the passage 71 communicates with a chamber orduct 73 directly below an entrance chamber 74 which communicatesdirectly with the intake opening 65 of the lower compartment. A damper75 is provided to control the communication between the chambers 73 and74, and, when it is open, air may pass directly from the intake 67 tothe inlet 65 and thence through the lower compartment of the preheater.Immediately above the chamber 74 is a similar chamber 76 which is indirect communication with the discharge opening 62- of the uppercompartment of the preheater and communication between the chambers 74and 76 is controlled by a damper 77. When this damper is open, airdischarged fromthe upper compartment through the opening 62 may passdownwardly into the chamber 74 and thence into the inlet 65 of the lowercompartment. The chamber 76' also communicates with a cross duct 78which opens directly into the discharge duct 68; communication betweenthe chamber 76 and the cross duct 78 may be provided upon opening of a.damper 80, and when this damper is open air discharged from the uppercompartment through the outlet 62 may pass directly from the outlettothe discharge duct 68. The outlet 66 from the lower compartmentcommunicates directly with a chamber 81 which is completely closedexcept for direct communication with the outlet duct 68. it will thus beapparent that the inlet opening 60I of the upper compartment is alwaysin communication with the system inlet 67, and the outlet opening 66 ofthe lower compartment is always in communication with the outlet 68 ofthe system.

The three dampers 75, 77 and 80 are operated simultaneously byconnection with an operating rod 82 actuated by a damper operating motor83. The dampers are connected. to the rod 82 so that when the dampers 75and 80 are open the damper 77 is closed, and vice versa. It will not beapparent that when the dampers 75 and are in their open positions andthe damper 77 is closed, as shown in FIG. 7, the air from the intake 67will enter both the upper and the lower compartments, and, as indicatedby the arrows, will pass around the baffles in the respectivecompartments where the air is heated and then flow out the respectivedischarge openings 60 and 66 from whence it will flow to the dischargeduct 68. This connection arranges the two compartments in parallel withrespect to the air flow.

When the dampers are moved to their opposite positions, as shown in FIG.8, with the damper 77 open and the dampers 75 and 80 closed, air fromthe inlet duct 67 passes upwardly to the top of the passage 71, asindicated by the arrows, and thence through the inlet 60 to the uppercompartment through which it flows and is heated; the heated air passesout through the outlet 62 downwardly through the opening about thedamper 77 thence through the inlet 65 to the lower compartment throughwhich it flows and is further heated and from which it is dischargedthrough the outlet 66 to the outlet duct 68. It will thus be apparentthat, when the dampers are in position with the dampers 75 and 80 closedand the damper 77 open, the two compartments are connected in series inthe air flow path, the air flowing first through the upper compartmentand then through the lower compartment before being discharged to theoutlet air supply. This arrangement assures a counterflow relationshipof the air and combustion gases when the two compartments are connectedin series since the coldest air passes first through the uppercompartment where the combustion gases are cooler and thence afterheating, through the lower compartment where the combustion gases are attheir highest temperatures.

Additional control of the preheater which facilitates its operation atlowloads is secured by providing a pair of hemispherical dampers and 86mounted on shafts 87' and 88, respectively, and which are positioned tocover a group of the tubes 27a in the center of the preheater. Thesedampers 85 and 86 are moved in unison so that both are either in theiropen position as shown in- FIG. 3 or in their closed position as shownin FIG.

6. The dampers may be moved from their open to their closed position byoperation of a motor 90- connected to drive the shaft 88 through a gear91 and the shaft 87 through a meshing gear 93 of the same size as thegear 91. The ends of the shafts 87 and 88 opposite the gears 91 and 92are mounted in bearings in a block 93. When the dampers are in theiropen position as shown in FIG. 3 the combustion gases rise through thecentral group of tubes and the heater may be operated at full capacity.Should the loadbe reduced the fiow of the combustion gases may berestricted to the outer tubes by closing the dampers 85 and 86; thismakes it possible to maintain the velocity of the combustion gasesthrough the tubes 27a although a reduced total volume of the gases isflowing.

Both the motors 83 and 90 are arranged so that the dampers of thepreheater may be controlled from a remote point, thus the operator maychange the control condition of the preheater whenever he desires to doso in orderto compensate for changes in the boiler load. From theforegoing, it is apparent that this invention provides a simple andeasily controlled preheater which makes possible the more efiicientoperation of the combustion equipment and boiler of a power plant.

Although the invention has been disclosed in connection with a specifictype of boiler construction other applications will readily be apparentto those skilled in the art. Therefore, it is not desired that theinvention be limited to the details of construction illustrated, anddescribed, and it is intended by the appended claims to cover allmodifications which fall within the spirit and scope of the invention.

I claim:

1. In a power plant or the like having burners for the combustion offuel and air and an outletfor thedis.-

7 charge thereof, an air preheater comprising spaced plates having aplurality of openings therein positioned to inter rupt the fiow ofheated gases, a plurality of open-ended tubes extending between saidspaced plates and in flow connection with matched openings through saidplates to provide a plurality of passages through which heated gases maypass,'mernbers joining the outer edges of said spaced plates forenclosing the tubes disposed between said plates, said members providingan inlet opening for the introduction of air flow between said platesand an outlet opening through which the heated air passing through saidpreheater may be removed, and bafiie means within said enclosureextending between said spaced plates for preventing direct flow fromsaid inlet opening to the outlet opening, said baffie meansbeingcooperatively placed within said enclosure toform a passage between saidinlet opening and said outlet opening of gradually increasing crosssectional area along the flow direction from the inlet to the outlet.

2. In a power plant or the like having burners for the combustion offuel and air and an outlet for the discharge thereof, an air preheatercomprising spaced plates having a plurality of openings thereinpositioned to interrupt the flow of heated gases, a plurality ofopenended tubes extending between said spaced plates and in flowconnection with matched openings through said plates to provide aplurality of passages through which heated gases may pass, membersjoining the outer edges of said spaced plates for enclosing the tubesdisposed between said plates, said members providing an inlet openingthrough which air may be introduced and an outlet opening through whichthe heated air passing through said preheater may be removed, and bafliemeans within said enclosure extending between said plates positioned toform a passageway between said inlet and outlet openings having a crosssectional area that increases in the direction of flow in an amountcorresponding to the amount of expansion per unit weight for the airover the temperature range existing between the inlet opening and theoutlet.

3. In a steam generating plant or the like of the type including anupright cylindrical structure serving the dual purposes of draft stackand boiler housing and providing an air and combustion products flowsystem comprising fuel burners adjacent the base of said structuretogether with means for introducing air through said burners and acentrally open passage upwardly through said structure through whichheated products of combustion rise under the influence of the high draftcreated by the combustion temperature of said products, the improvementwhich comprises an air preheater positioned within said structure abovethe steam producing elements thereof, said preheater comprising aplurality of open-ended tubes aligned with the flow direction of saidcombustion products through the central passage, conduits forintroducing air through the side face of the cylindrical structureadjacent the air preheater, bafiie means interiorly of said preheaterforming a passage therethrough adapted to direct the incoming air incontact "with said tubes to the center of said preheater and thenceoutwardly to a point of discharge at the side face of the structure,said passage being of gradually increasing cross sectional area as theair is heated, and conduit means for receiving said heated air at thepoint of discharge and delivering said heated air to the point of use.

4. In a power plant or the like having burners for the combustion offuel and air and an outlet for the discharge thereof, an air preheatercomprising spaced plates having a plurality of openings thereinpositioned to interrupt the flow of heated gases, a plurality ofopen-ended tubes extending between said spaced plates and in flowconnection with matched openings through said plates to provide aplurality of passages through which heated gases may pass, membersjoining the outer edges of said spaced plates for enclosing the tubesdisposed between said plates, a partition plate positioned intermediatesaid spaced plates for dividing the space therebetween into twocompartments, said members providing inlet openings for the introductionof air to each compartment and outlet openings through which the heatedair passing through said compartment may be removed, and baflle meanswithin each of said compartments extending between said partition andthe respective ones of said spaced plates for directing the passage ofair from the inlet to the outlet of each of said compartments, saidbaflle means being arranged in each compartment to form a passage fromthe inlet to the outlet thereof having a gradually increasing crosssectional area along the flow direction from the inlet to the outlet,the inlet'and outlet opening of each of said compartments beingoppositely positioned with respect to the openings of the othercompartment whereby the air flows through said compartments incounterflow relationship.

5. An air preheater for a power plant or the like as set forth in claim4 including means providing an inlet air connection and an outlet airconnection and means includ ing dampers movable to one position forconnecting said compartments in series between said inlet and outletconnections and to a second position for connecting said compartments inparallel between said connections.

6. An air preheater for a power plant or the like as set forth in claim4 including means providing an inlet air connection and an outlet airconnection, and means including dampers movable to one position forconnecting said compartments in series between said inlet and outletconnections and to a second position for connecting said compartments inparallel between said connections, said damper means when in position toconnect said compartments in series directing the air from said inletconnection to the inlet of the one of said compartments adjacent theoutlet end of said tubes and from the outlet of said one compartment tothe inlet of the other of said compartments, whereby the air is directedin counterflow relationship to the gases passing through said tubes.

7. An air preheater for a power plant or the like as set forth in claim1 comprising means including a damper positioned adjacent the outlets ofa plurality of said tubes less than the total number of tubes andarranged to cut off the flow of gas through said plurality of tubes forproviding two alternative conditions of operations to control the flowof hot gases through said preheater.

8. In a power plant or the like having burners for the combustion offuel and air and an outlet for the discharge thereof, an air preheatercomprising a cylindrical casing, a pair of spaced plates mounted in saidcasing transversely thereof to form a compartment therein, each of saidplates having a plurality of openings positioned in matched pairs, aplurality of open-ended tubes extending between said spaced plates andeach connected between a pair of matched openings through said plates toprovide a plurality of passages through which heated gases may pass,means for supporting one of said plates rigidly with respect to saidcasing, means including an expansible seal connected between said casingand the other of said plates for affording movement of said other platelongitudinally with respect to said casing, means providing an air inletand an air outlet for said compartment between said plates, and bafliemeans within said compartment extending between said plates forpreventing direct flow from said inlet opening to said outlet opening,said bafiie means being positioned to form a passage between said inletopening and said outlet opening of gradually increasing cross sectionalarea along the flow direction from the inlet to the outlet.

9. A heat exchange and gas treating unit for power plants and the like,comprising an uprightsubstantially cylindrical casing, a heat exchangeelement comprising a pair of spaced plates within and extending acrosssaid casing to provide a compartment therein, each of, said plateshaving a multiplicity of holes therethrough, a plurality of tubes insaid compartment each connecting corresponding holes in said plates andproviding passages through said plates and across said compartment,means for conducting a fluid across said tubes within said compartmentfor heat exchange with fluid flowing through said tubes, means includinga frusto-conical partition section in said casing above said heatexchange element for providing an annular closed chamber about thecenter of said casing, means for directing the fluid flowing from saidtubes alternatively through said chamber or directly out of said casing,and hanger means for supporting said heat exchange element from saidfrusto-conical partition section.

References Cited in the file of this patent UNITED STATES PATENTS GrahamMar. 25, 1884 Leman May 5, 1903 Black Dec. 16, 1930 Brantly Aug. 4, 1942Artsay Oct. 9, 1945 Stahn et a1 Sept. 29, 1953 Bliss Nov. 15, 1955Campbell Jan. 31, 1956 Howes May '8, 1956 MacAfee et al June 19, 1956Frisch Aug. 6, 1957 Miller Dec. 24, 1957

